Filament lamp lighting devices are widely used for heat treatment and general lighting. Light irradiation heat treatment equipment for semiconductor wafers (hereafter wafers) can be cited as one application of filament lamp lighting devices to heat treatment.
Heat treatment is used in the process of semiconductor manufacturing for rapidly heating wafers, maintaining them at a high temperature, and rapid cooling. It is carried out in a broad range of processes such as film formation, diffusion and annealing.
In all the above processes, the wafer is treated at a high temperature, and when this heat treatment is done using light irradiation heat treatment equipment, the wafer can be heated rapidly, exceeding 1000.degree. C. in 10 to 30 seconds. And when the light irradiation is stopped, rapid cooling is possible.
However, if the temperature distribution of the wafer is uneven when the wafer is heated, the phenomenon known as slip occurs in the wafer. In other words, defects occur in the crystal dislocation, and poor quality products are liable to result.
Therefore, when using light irradiation heat treatment equipment for heat treatment of wafers, it is necessary that the heating, temperature maintenance and cooling of the wafer be done with uniform temperature distribution.
Light irradiation heat treatment equipment intended to irradiate so that the temperature distribution of the wafer will be uniform includes, for example, that presented in JPO kokai patent report H8-45863. The light source of the light irradiation heat treatment equipment described in that report had a number of ring-shaped infrared lamps of different diameters arranged in concentric circles. By arranging the lights in that way, the wafer could be divided into concentric zones, and temperature control was simplified.
To make the temperature of the wafer uniform, the temperature of each zone of the wafer was measured and the heat generated by the infrared lamp corresponding to each zone was controlled accordingly. That is, if the temperature were lower at the periphery of the wafer, the input power to the lamp covering the center of the wafer would be increased, and the amount of heat generated by the lamp would go up and apply more heat to the wafer. The variation of the heat generated by the lamp is referred to below as "light adjustment."
Halogen lamps with filaments that radiate infrared light efficiently are generally used as the infrared lamps in light irradiation heat treatment equipment. Moreover, an alternating current power supply is generally used as the lighting power supply.
Light adjustment of filament lamps is done in the following way.
(1) For light adjustment of a filament lamp in a general lighting fixture, a circuit with a triac is normally used, and adjustment is done by controlling the continuity angle of the triac. PA1 (2) Light adjustment of light irradiation heat treatment equipment basically applies the same circuit, and so a thyristor is used. The basic structure of lamp lighting device using thyristors is shown in FIG. 9. Now, one lamp lighting device is used for a single lamp. Consequently, in equipment to control the lighting of multiple lamps, the number of lamp lighting devices depends on the number of lamps. The devices are housed on the equipment power supply box. PA1 1) In practical terms, in equipment such as light irradiation heat treatment equipment, when there is, for example, a commercial 200 V input to the lamp lighting device, then considering a 10% voltage fluctuation it is common sense to use a lamp with a rated input voltage that is 10% lower, 180 V for example, to leave an adequate margin. Consequently, the power of the lamp lighting device is controlled even when lighting the lamp at the rated value. PA1 2) In light irradiation heat treatment equipment, moreover, the lighting and light adjustment of multiple lamps may, depending on the lamps used, involve different ratings (different filament lengths). In this case as well, the output power is always controlled.
In the lighting device shown in FIG. 9, control of the power input to the lamp, or light adjustment, is done by varying the timing of the gate current of thyristors SCR1 and SCR2.
Power control by thyristor is done by two methods, continuity angle control and zero cross control. Now, terminology is defined below. Input power from a commercial alternating current power supply to the lamp lighting device is called "input." The power output from the lamp lighting device to the lamp is called "output." Accordingly, "output power" is "lamp input power."
(a) Continuity Angle Control
In FIG. 9, alternating current from a commercial alternating current power supply 21 is input to the lamp lighting device 100. Within the lamp lighting device 100 is a lamp lighting control circuit 200 that comprises the first thyristor SCR1 and the second thyristor SCR2. When the gate signal generated by the gate signal generation circuit of the controller 300 lets the gate current flow to the gates G1, G2 of the thyristors SCR1, SCR2 of the lamp lighting control circuit 200, then current is output from the lamp lighting device 100 to the lamp 23 until the current supplied to the thyristors SCR1, SCR2 of the lamp lighting control circuit 200 becomes zero.
FIG. 10 is a diagram showing the various waveforms in the event of continuity angle control of the thyristors in FIG. 9. FIG. 10(a) shows the input voltage waveform to the lamp lighting device 100. FIG. 10(b) is a diagram showing an example of the timing of the gate current flow to the gates G1, G2 of the thyristors SCR1, SCR2, in which (1) is the gate current for the first thyristor SCR1 and (2) is the gate current for the second thyristor SCR2. FIG. 10(c) shows the waveform of the output current when the gate current flows with the timing from FIG. 10(b). Now, in the case of filament lamp lighting devices, the output voltage has the same waveform as the output current.
Consequently, the output power from the lamp lighting device 100 is the product of the out current waveform and the output voltage waveform shown by the shaded area of FIG. 10(c). By varying the timing of the gate current supplied to the thyristors SCR1, SCR2, it is possible to vary the output voltage waveform an output current waveform shown in FIG. 10(c), and so light adjustment that varies the output power, which is the lamp input power, is possible.
(b) Zero Cross Control
FIG. 11 is a diagram showing the various waveforms in the event of zero cross control of the thyristors in FIG. 9. The structure of the control circuit is the same as FIG. 9, and the timing of the gate current to the thyristors SCR1, SCR2 is as shown in FIG. 11(b). In the figure, (1) is the gate current for the first thyristor SCR1 and (2) is the gate current for the second thyristor SCR2.
FIG. 11(c) shows the output current and output voltage when the gate current has the timing shown in FIG. 11(b). As shown in FIG. 11(c), the lamp input voltage is varied and light adjustment is carried out by means of intermittence of output current and output voltage waveforms.
However, the two control methods described above have the following problems.
(1) Occurrence of Transient Noise (Continuity Angle Control)
In the continuity angle control method illustrated in FIG. 10, a high voltage is suddenly impressed on the lamp as shown in FIG. 10(c). Because of that, noise known as transient noise occurs within the lamp lighting device, and that sometimes causes the device control system to malfunction. And because of a rush current flow in the lamp filament, the filament is in a state of overload, which is liable to cause filament breakage.
(2) Drop in Response Speed; Lack of Constant Control (Zero Cross Control)
In the case of zero cross control, the voltage of the power source is sent through the thyristor at the time of the zero cross, so a high voltage is not impressed suddenly on the lamp. Nevertheless, the cycles of the commercial input frequency are thinned out as shown in FIG. 11(b) so the response time of the light adjustment cannot be faster than the frequency of the commercial power supply, and rapid light adjustment is not possible. Moreover, the output power cannot be varied continually, and so minute light adjustment is not possible.
(3) Occurrence of High-frequency Distortion
Taking the example of continuity angle control shown in FIG. 10, when the power control is done on the output side, as described above, the output voltage and output current are as shown in FIG. 12(a) and (b) respectively.
On the other hand, the waveform of the input voltage to the lamp lighting device 100 is the voltage waveform of the commercial alternating current power supply shown in FIG. 12(c). The waveform of the input current, moreover, is the same as the waveform of the output current, as shown in FIG. 12(d).
The following problem occurs when the input current has this kind of waveform. The parts of the waveform indicated by the circles in FIG. 12(d) are nonlinear, and that causes high-frequency distortion of the input current. This sort of high-frequency distortion is becoming the object of regulation.
A similar problem occurs in the zero cross control illustrated in FIG. 11. The parts of the waveform indicated by the circles in FIG. 12(e) are nonlinear, and high-frequency distortion occurs.
(4) Occurrence of Reactive Power
In FIG. 12, input voltage is V and input current is I. When W is effective power and V.times.I is apparent power, the input voltage waveform and the input current waveform are both sine waves, and are in the following relationship unless there is a phase shift. EQU V.times.I=W
W can be thought of as the output power (lamp input power).
However, in the case of a distorted waveform, as in FIG. 12(d), there is always reactive power (=V.times.I-W). Consequently, in the distorted waveform shown in FIG. 12(d), in order to output effective power W, it is necessary to supply an apparent power V.times.I that is greater than the sine wave.
Similarly in the case of zero cross control, reactive power occurs because the period shown by the arrows in FIG. 12(e) is considered one cycle.
This reactive power occurs as soon as the output power is controlled. This fact is a big problem when practical equipment is manufactured.
That is, for the reasons given below, the output power of the lamp lighting device 100 is always controlled, so there is necessarily reactive power in the lamp lighting device 100, which harms the efficiency of the lamp lighting device.
However, an alternating current chopper control method has been proposed as a method to resolve this problem of reactive power. The alternating current chopper control method is one which controls the output voltage (current) by chopping the input voltage (current) with a switching circuit. By controlling the ON period in the switching operation, it is possible to control the output voltage (output current).
Parts of the waveform when the alternating current chopper control method is in use is shown in FIG. 13.
That is, the input voltage (current) shown in FIG. 13(a) is turned ON/OFF by the switching signal shown in FIG. 13(b), yielding the output current shown in FIG. 13(c). Now, the figure shows a duty cycle of about 50%. In the constitution used here, the switching circuit used for commutation is in parallel with the load, and the inductance is in series with the filament lamp, so when the switching circuit connected in series with the input side is off, the switching circuit for commutation is on, and the output current flows continuously through the commutation circuit.
With the waveform shown in FIG. 13(c), if the frequency of the switching signals is increased, the waveform becomes closer to a sine wave, and by applying further filtering to the output current shown in FIG. 13(c), it is possible to obtain the sinusoidal output shown in FIG. 13(d). The input current can also be made sinusoidal by passing it through a low-pass filter.
Using the alternating current chopper control method described above, it is possible to have sinusoidal input and output waveforms and, since the phase of the voltage and current is the same, there is no problem of reactive power.
Moreover, since there is no sudden rise of output current, the problem of rise noise does not occur, and by controlling the duty cycle of the switching signals, rapid and minute light adjustment is possible.
As stated above, in a lamp lighting device that controls the heat generated by a filament lamp by varying the power input to the lamp, it is necessary to vary the output power so as to not impress voltage on the lamp suddenly (to avoid producing noise and to avoid a large rush current to the lamp), and so as to enable continuous light adjustment with a rapid response time. It is also necessary to vary the output current such that there is no high-frequency distortion of the input current and no reactive power.
When the alternating current chopper control method described above is used, it is possible to make the output current, output voltage and input current waveforms sinusoidal, and so continuous light adjustment with a rapid response time is possible with no occurrence of reactive power and without large rush currents being passed suddenly to the lamp.
Nevertheless, the alternating current chopper control method does cause high-frequency distortion of the input current unless there is a filter circuit on the input side since, as shown in FIG. 13, the switching signals shown in FIG. 13(b) turn the input voltage (current) ON and OFF.
In light irradiation heat treatment equipment, in particular, light adjustment of multiple filament lamps is necessary and the input current to be switched is large, so high-frequency distortion has a great effect on the power supply side.
This invention was made in consideration of the situation described above. It provides a filament lamp lighting device that has an alternating current power supply connected to the input side and lights multiple filament lamps by controlling its output power, in which either there is no need for a filter circuit to eliminate high-frequency distortion on the input side, or it can be miniaturized so that the power supply side is unaffected by high-frequency distortion.